Overfeeding protein is a common concern when grazing milkers on lush,
well-managed pastures. But milk urea nitrogen (MUN) analyses can help you
determine if that's the case. If it is, adjusting rations accordingly may
reduce your feed costs, increase production, avoid ketosis, improve body
condition, boost reproductive performance and help keep nitrates out of surface
and groundwater, says Dr. Larry Chase, a dairy nutrition specialist with Cornell
Cooperative Extension. Chase is working with NRCS grazing specialist Darrell
Emmick and Extension nutritionist Karen Hoffman comparing MUN levels on pasture
and during confinement feeding in more than a dozen herds around the state this
year.

When cows consume too much protein, they must expend extra
energy to convert excess ammonia to urea, explains Chase. Urea levels in their
blood, plasma and milk rise. MUN samples are relatively inexpensive and simple
to take, and performed correctly can provide a good index of your herd's protein
status, he adds.

While MUN research -- especially on pasture -- is
still in its infancy, values in the 12 to 16 mg/dl range are considered normal.
Readings below that indicate that you should probably increase total and soluble
protein in supplemental feeds. Higher values suggest that you should decrease
the protein in your rations, or simultaneously feed more high-energy
carbohydrate sources, so that the energy is available when rumen microbes need
it most.

Don't use MUN tests to try to analyze individual cows,
cautions Chase. Sample milk from at least 10 animals grouped by production
level, lactation stage or ration. Follow sampling instructions carefully,
including prompt refrigeration or the addition of a fermentation inhibitor.

Also, don't base ration changes solely on MUN values, warns Chase.
Work with your feed advisory or veterinarian to use MUNs as another tool to
fine-tune your feeding program, he suggests. For more information about MUN
testing, contact Northeast DHIA at (800) 344-2697.